Fertigation-fertilization effects on microirrigated Florida flatwoods grapefruit

Material Information

Fertigation-fertilization effects on microirrigated Florida flatwoods grapefruit
Series Title:
Ft. Pierce AREC
Boman, Brian J
Agricultural Research and Education Center (Fort Pierce, Fla.)
Place of Publication:
Fort Pierce Fla
University of Florida, Insititute of Food and Agricultural Sciences, Agricultural Research and Education Center
Publication Date:
Physical Description:
3 leaves : ; 28 cm.


Subjects / Keywords:
Grapefruit -- Fertilizers -- Florida ( lcsh )
Grapefruit -- Irrigation -- Florida ( lcsh )
Microirrigation -- Florida ( lcsh )
Irrigation ( jstor )
Fertilization ( jstor )
Agricultural seasons ( jstor )
non-fiction ( marcgt )


General Note:
Caption title.
Statement of Responsibility:
Brian J. Boman.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
66526310 ( OCLC )


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The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida


Brian J. Boman
Associate Professor, Agricultural Research and Education
Center, P.O. Box 248, Ft. Pierce, Florida 34954.

A four-year field experiment was conducted to determine
the effects of microsprinkler irrigation management practices
on the fruit production and juice quality of mature 'Ruby Red'
grapefruit on sour orange rootstock trees in a Flatwoods
grove. The trees were in a grove located about 15 miles west
of Ft. Pierce on 50 ft double-row beds on a Pineda series
soil. Tree spacing was 20 ft within-row by 25 ft across-row,
resulting in a density of 87 trees ac-1.
Trees were irrigated with microsprinkler emitters which
wetted areas 11, 15, 19, and 23 ft in diameter, resulting in
19, 35, 57, and 83% of the orchard floor wetted. Irrigations
were initiated when soil tensions reached 10-15 cbar (L-DEPL)
or 35-45 cbars (H-DEPL), corresponding to about 33% and 50%
depletion of soil moisture. The L-DEPL irrigations occurred
every 2-3 days during the spring irrigation season while the
H-DEPL irrigations were applied every 4-6 days.
Fertilization was either by conventional broadcast
* application 3 times per year (DRY-3) or by a combination of
broadcast and fertigation (FERT). The DRY-3 plots received
40% of the annual N and K (plus minor elements) during an
application in late winter (February/March plus additional
applications, each with 30% of the annual N and K in the
May/June and October/November time periods. The FERT plots
received 40% of the N and K requirements (plus minor elements)
with a dry broadcast application in February. The remaining
60% of the N and K on the FERT plots was applied throughout
the season as a liquid injected with the irrigation water
approximately every 2 weeks from April through early November.
Both the liquid and dry broadcast fertilizer material were
derived from NH4NO3 and KC1 sources, with 150-160 lb ac- of N
and K applied per year.
The experiment was conducted as a randomized complete
block design with 5 replications of each treatment. Plots
typically consisted of 8-10 trees, with yield measurements
taken on the middle across-bed pairs in each plot. The
factors evaluated in the experiment were: microsprinkler
coverage diameters (4), the soil moisture tension at which
irrigations were initiated (2), and fertilization practices
(2). Only results pertaining to the fertilization treatments
are presented in this summary.
The first 2h years of the study was one of the driest
periods in recent times in Florida. Only 34.5 inches of
* rainfall were recorded in 1988, followed by 36.8 inches in
1989. The first half on 1990 was also very dry. However,

Ft. Pierce AREC 93-8

summer rains brought relief to the extended drought. The 1990
rainfall total was 42.8 inches and in 1991 the total was 56.3
inches. Two major temperature-related factors affecting
production occurred in 1989. The first occurred on February
24, when the temperature dropped to 270F. The sub-freezing
temperatures came during the peak of the bloom. The effects
were a much-reduced fruit set throughout the area during the
year. The other significant climatic event affecting citrus
was the December 1989 freeze when temperatures dropped to
230F. Most of the damage to the grapefruit trees was confined
to dropping about one third of their leaves and necrosis of
the smaller twigs. The fruit had been picked in early
December, so there was no fruit on the trees to be damaged.
Only minor differences were noted with respect to leaf
mineral content due to fertilization. The FERT plots had
higher leaf N content in 1 of 3 years (1989: 2.7% compared to
2.5%), and lower K in 1 of 3 years (1991: 0.90% versus 0.97%).
Other elements had non-significant differences.
The only differences in juice quality between treatments
occurred during the first yer of the study when their FERT
fruit was larger, had lower Brix, and lower solids per box
than the DRY-3 treatment fruit (Table 1).

Table 1. Significance of measured yield and juice quality
parameters for fertilization treatments (n-40 ).
Parameter 1988/89 1989/90 1990/91 1991/92 Total
Fruit weight ns ns ns --
Juice Z ns ns ns ns --
Acid ns ns ns ns --
Brix ** ns ns ns --
Ratio ns ns ns ns --
Solids/box ns ns ns ns
Boxes/tree ns **
Solids/tree ns ns ns ** **
Note: ns non-significant differences, significant
difference between means at P-0.05, ** significant
difference between means at P+0.01).

During the four-year period, the FERT trees out-produced
the DRY-3 trees in 3 of the years in terms of boxes (Fig. 1)
and had higher solids production in one year (Fig. 3). The
cumulative advantage of the FERT trees was highly significant
for both boxes and solids (P=0.01). The cumulative yield for
the FERT trees was 2071 boxes per acre compared to 1897 for
the DRY-3 treatments (Fig. 2). The difference of 174 boxes
per acre in the four-year period averages to a remarkable 44
boxes per acre per year advantage for the FERT program. The
cumulative solids produced over four years for the FERT trees
averaged 9744 lbs per acre versus 9048 lb per acre for the
DRY-3 treatments (Fig. 4). The difference of 686 lbs averages
to about 172 Ib greater solids per acre per year for the FERT
compared to the DRY-3 treatments.

Ft. Pierce AREC 93-8


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Fig. 1. Average fruit yield by season
for FERT compared to DRY-3 treatments
(n=40, means with an are significantly
different at P=0.05).

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1989/90 1990/91

1988/89 1980/90 1t9o0/1 1991/02

Fig. 3. Average solids produced by season
for FERT compared to DRY-3 treatments
(n=40, means with an are significantly
different at P=0.05).

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. 6

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Fig. 2. Cumulative yield advantage of
FERT over DRY-3 treatments for the 1988/89
through 1991/92 seasons (n=40, advantage =
FERT yield DRY-3 yield).


1989/90 1990/91






Fig. 4. Cumulative solids advantage of
FERT over DRY-3 treatments for the 1988/89
through 1991/92 seasons (n=40, advantage =
FERT yield DRY-3 yield).